1. Field of the Invention
The present invention relates to a light signal transmission system wherein signals are transmitted by means of light by interconnecting a plurality of terminal stations to each other.
2. Related Background Art
Nowadays, a light signal transmission system wherein light signals are coupled between local area networks has widely been popularized. Topology of the light signal transmission system includes a star-shaped arrangement, bus-shaped arrangement, loop-shaped arrangement or the like; among them, the loop-shaped arrangement has widely been used because of having various advantages. As shown in FIG. 1, the loop-shaped arrangement includes an annular signal transmission path obtained by interconnecting a plurality of terminals (stations) 39 through optical fibers 40. The loop-shaped arrangement has a representative advantage that a load of the transmission/reception module is small since the transmission between the terminals can be performed by transmitting the signal between only two points, thus simplifying the construction of the system.
However, in the signal transmission system of the loop-shaped arrangement, since it is necessary to form a closed loop or path by means of the transmission lines, there arises a problem that, when the terminal stations are installed, such a closed loop must previously be considered, thus reducing the freedom or flexibility for installing such terminal stations. This problem will particularly be serious or critical when the network is expanded to obtain the more complex signal transmission path in a limited space in an intelligent building or the like. For example, as shown in FIG. 2, when a plurality of stations 39a-39f are installed in order or needed and two adjacent stations are interconnected by means of an optical fiber line 40a, in order to form a closed loop, a return optical fiber line 40b for returning the signal from the last terminal station 39f to the start terminal station 39a must be prepared. Therefore, not only the need of the installation of the stations but also the signal return path must always be considered. Accordingly, while the signal transmission system of the loop-shaped arrangement was excellent in function, it arose a problem that the installation of the terminal stations thereof was limited.